1. Field of the Invention
The present invention relates to a plasma processing method using a plasma processing apparatus used for manufacturing semiconductor devices.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, ashing processes are performed to remove resist films and organic films used as mask. Conventionally, ashing has been performed after an etching process in a dedicated ashing device designed separately from an etching apparatus. However, from the viewpoint of reducing processing time, there are demands to realize continuous etching and ashing in the same apparatus.
However, when etching is performed using fluorocarbon gas as main component used mainly for processing insulating films, CF-based films are deposited on the side wall of the reaction chamber. When ashing is performed in this state, the fluorine released when removing the CF-based deposits enter the wafer and cause fluctuation of dimension. Such phenomenon is called a memory effect, since the effect of a past process performed prior to ashing affects the process.
Japanese patent application laid-open publication No. 11-145111 (patent document 1) provides a method for performing ashing in two stages in order to suppress such memory effect. As disclosed in the flowchart of patent document 1, at first in the first stage, oxygen plasma is generated without applying wafer bias, to thereby remove the deposits on the side wall of the reaction chamber. Thereafter, wafer bias is applied to remove the resist films or the like on the wafer.
Japanese patent application laid-open publication No. 2007-80850 (patent document 2) discloses another method for performing ashing in two stages, wherein carbon dioxide plasma is used instead of oxygen plasma so as to suppress damage.
Other prior art methods are disclosed in Japanese patent application laid-open publication Nos. 2001-110783 (patent document 3) and 2008-03449 (patent document 4).
The prior arts mentioned above adopt a method in which the fluctuation of dimension is suppressed by not applying any wafer bias during removal of deposits on the side wall of the reaction chamber. However, in all the prior arts, upon removing the deposits on the side wall of the reaction chamber, plasma similar to that used during ashing performed thereafter by applying wafer bias is generated above the sample to be processed, and the fluorine released from the side wall of the reaction chamber during cleaning of the wall diffuses over the wafer, causing possible fluctuation of dimension. Further, even when carbon dioxide plasma is used, the fluorine diffused from the wall may enter the wafer, and this problem cannot be sufficiently overcome by simply not applying wafer bias. According to the above-mentioned prior arts, damage to the low-k films may occur, or etching of the underlayers (liners) may occur.